We propose to use computer simulation techniques to obtain detailed information relating to the conformation of cyclic polypeptide molecules. Of particular interest are relatively small (5 or 6 residue) synthetic polypeptides which are known to bind positive metal ions and which may serve as simple prototypes of biological molecules, such a valinomycin and other transport antibiotics, which can carry ions across membranes. The polypeptides are also relevant to our understanding of the transport function of membrane proteins. The simulation methods to be employed will include harmonic analysis and molecular dynamics. From these calculations we can study the structural and thermodynamic changes accompanying the conformational transformations associated with ion binding. In particular, the information to be gained from the computer models will include the molecular conformations of lowest energy for both the free and bound polypeptide, the energy and entropy of ion binding, the vibrational normal mode frequencies, and the magnitudes, time dependence, and correlations of internal structural fluctuations. Considerable insight will thus be obtained about the molecular mechanisms of ion transport in membranes.